Surgical procedures cause damage to tissues and cells from the invasion of surgical instruments, tissue/tissue contact and the intraocular irrigation media. This invasion can result in the destruction of cells and tissues which can lead to various medical complications. Accordingly, the protection of tissues and cells during surgery is of paramount importance, particularly in ophthalmic surgery owing to the sensitivity of the tissue and cells comprising the eye. During intraocular surgery it is often necessary to flush the anterior chamber and/or maintain the fluid volume in the anterior chamber.
In order to prevent damage to the tissues and cells of the eye, it is known to continuously bathe the eye with liquids which approximate the composition of the body fluids. Early tissue irrigation solutions contained sodium, potassium, calcium and chloride ions having an isotonic electrolyte content. These solutions, however, were of limited success because they did not sufficiently prevent swelling and consequential damage to ocular tissues.
There was also developed a number of irrigation solutions which sought to mimic the composition of the aqueous humor of the eye. The first of these solutions was known as Ringer's solution which included sodium lactate in addition to the electrolytes used in the isotonic electrolyte solution.
A further type of tissue irrigation solution is known as a balanced salt solution (BSS) which contains sodium, potassium, calcium and magnesium ions and an acetate-citrate buffer system.
An additional tissue irrigation solution was developed which combined the Ringer's solution with glutathione and sodium bicarbonate. This solution, known as Glutathione Bicarbonate Ringer Solution (GBR), has been employed as a tissue irrigation solution (B. E. McCarey et al., "Functional and Structural Changes In The Corneal Endothelium During In Vitro Perfusion", Invest. Ophthalmol., 12:410-417 [1973]).
More recently, dextrose and sodium hydrogen phosphate have been added to GBR to obtain an enhanced balanced salt solution (commonly called "BSS Plus").
The irrigation solutions described above suffer from a number of disadvantages. Most importantly, such solutions must be prepared at the site of use from two separate mixtures. This is because the bicarbonate and phosphate ions precipitate in the presence of magnesium and calcium ions. In addition, the bicarbonate and the glutathione tend to decompose within the pH range typically associated with irrigation solutions.
It would therefore be desirable to have a tissue irrigation solution that closely approximates the composition of the tissues to which it is applied (e.g. the aqueous humor) and is sufficiently stable so that it can be packaged and used as a one-part solution without mixing as required by two-part GBR solutions.